Domestic Fowl

Abstract

It is thought that birds evolved from early reptiles, perhaps dinosaurs, in the upper Jurassic Age (150 MYA). Ayes have spread worldwide and developed some 8000 species. They are unique in being covered with feathers, having a warm body temperature (40–43°
C), laying hard-shelled eggs, and nurturing their young. Their bodies are streamlined, with beaked heads, flexible necks, two forelimbs that are wings, and two weight-supporting hindlimbs. Most birds have four toes that end in horny claws. Birds also have tails composed primarily of feathers, which, together with the wings and light skeletons, make flying possible. To obtain energy for flying, birds must eat almost continually. Their diet varies with their habitat—seeds, berries, insects, and small fishes or animals are common food.